Fuel control systems are known which compensate for fuel delay caused by slow fuel vaporization during cold engine operation by utilizing a predetermined delay model which alters the amount of fuel injected according to engine temperature. As the engine warms up, different values are obtained from the delay model to reflect the increased fuel vaporization rate. Such models typically store information as a function of engine coolant temperature which correlates generally with the temperature of metal contacted by fuel as it is injected and hence correlates generally with fuel vaporization rate.
In practice, a portion of the injected fuel directly impacts the intake valve which, because it is less affected by the engine coolant temperature, warms up at a different rate than the walls of the induction system. Fuel directly impacting the intake valve vaporizes at a different rate than that predicted by the model. Consequently, model values based on engine coolant temperature lead to inaccurate quantities of fuel being delivered during engine warm-up, which leads to poor engine performance.